Two-piece channel diffuser

ABSTRACT

A channel diffuser for a centrifugal compressor in which the diffuser is formed from two annular elements, sandwiched together. One element is a flangelike portion of the outer housing for an engine and has a smooth radially extending face. The second element has a series of tangentially directed channels open toward the radial face on the first element to form diffuser passages. The channels in the second element diverge both in width and in height so that all the divergence in the passages is provided by the channels.

nited States Patent 1191 Stein et a1.

[ Mar. 25, 1975 TWO-PIECE CHANNEL DIFFUSER [75] Inventors: Wolfgang J.Stein, Milford;

Salvatore Straniti, Orange; John T. Exley, Milford, all of Conn.

[73] Assignee: Avco Corporation, Stratford, Conn.

[22] Filed: Nov. 29, 1973 [21] Appl. No.; 420,201

152] US. Cl. 415/207 [51] Int. Cl. F04d 29/44, FOld 9/04 [58] Field ofSearch 415/207, 211, 82, 210, 415/181; 60/3926 [56] References CitedUNITED STATES PATENTS 1,879,561 9 1932 Smith 415/211 2,042,550 6/1936Poffer 415/211 3,027,717 4/1962 Conklin 415/211 3,088.279 5/1963Diedrich 60/3936 3,305,165 2/1967 Gregory 415/207 3,489,339 1/1970Greenwald... 415/211 3,658,437 4/1972 Soo .1 415/207 PrimaryEraminer-William L. Freeh Assistant Examiner-Louis J. CasaregolaAttorney, Agent, or Fi1'n1Charles M. Hogan; Gary M. Gron; lrwin P.Garfinkle [57] ABSTRACT A channel diffuser for a centrifugal compressorin which the diffuser is formed from two annular elements, sandwichedtogether. One element is a flangelike portion of the outer housing foran engine and has a smooth radially extending face. The second elementhas a series of tangentially directed channels open toward the radialface on the first element to form diffuser passages. The channels in thesecond element diverge both in width and in height so that all thedivergence in the passages is provided by the channels.

9 Claims, 3 Drawing Figures TWO-PIECE CH ANNEL DIFFUSER The presentinvention relates to compressor diffusers and more particularly tocompressor diffusers for radialtype compressors.

One of the most important components of a centrifugal compressor is thefixed diffuser section which receives the high velocity air dischargedfrom a rotating impeller. This component is designed to diffuse the highvelocity and increase its static pressure to a level suitable for use inthe combustor of a gas turbine. Many different aerodynamicconfigurations have been proposed and adopted in the past to give themost efficient performance possible for a diffuser of this type.

One type of diffuser that is particularly advantageous is a so-calledchannel diffuser in which a series of vanes, extending betweenflangelike faces, form a series of tangentially directed diffuserpassages. This type of diffuser gives good performance but it fails toprovide sufficient divergence for the very high pressure increasesdesired in an advanced gas turbine engine. In addition, it is veryexpensive to manufacture and requires time-consuming manufacturingtechniques. The reason for this is that each blade must be secured atits ends to both walls of the diffuser by welding.

The above ends are solved in accordance with the present invention by acompressor diffuser having a first annular clementthat has asubstantially smooth face defined by an inner and outer diameter. Theface is defined by straight-lined elements extending radially from theinner to the outer diameter. A second annular element abuts the face onthe first element and has a plurality of tangentially directed channelsopen to the face to form a series of diffuser passages. The channelshave an increasing cross-sectional flow area defined by an increasingchannel height and width so that all of the divergence in the diffuserpassages takes place in the channels formed in the second element.

The above and other related features of the present invention will beapparent from a reading of the following description of the disclosureshown in the accompanying drawing and the novelty thereof pointed out inthe appended claims.

In the drawings:

FIG. I is a longitudinal, simplified section view of a gas turbineengine which has a compressor diffuser embodying the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of the diffuserof FIG. ll, taken on line 22 of FIG. 1; and

FIG. 3 is a fragmentary cross-sectional view of the diffuser of FIG. ll,taken on line 3-3 of FIG. 2.

Referring to FIG. 1 there is shown a gas turbine engine comprising anoutput gearbox which supports an annular inlet housing 12. Inlet housing12 forms a bellmouth 14 to provide an annular inlet for ambient air intoa compressor 16. Compressor 16 comprises an axially bladed hub 18,stator vanes 20 and a centrifugally bladed impeller 22. Hub l8 andimpeller 22 are mounted on a central shaft 24 journaled for rotation atits upstream end by bearing assembly 26. The eompres-. sor I6pressurizes and accelerates air for discharge radially outward through acompressor diffuser, generally indicated at 28, whose construction willbe described in detail below. Air leaves the diffuser 28 with asubstantially tangential component. Vancs 29, secured between inner andouter annular duct walls 31, 33, turn air to an axial direction fordischarge into a chamber 30. Chamber 30 is formed by an outer housing 32which mounts duct wall 33 and an inner cast strut assembly 34. Aperforated combustor 36 in chamber 30 receives metered fuel from nozzles38 for mixture with air passing inward through the perforations. Themixture is ignited by a suitable device and the resultant hot gas streamis turned by a turbine inlet duct 40 for discharge from a turbine inletnozzle 42. The hot gas stream then passes across a bladed turbine rotor44 also secured to shaft 24. A bearing assembly 46. supported by strutassembly 34, journals shaft 24 adjacent turbine rotor 44. From there thehot gas stream passes across a bladed power turbine rotor 48 whichdrives a gear set in the output box through a power turbine shaft 50.

The diffuser 28 forms an extremely important component of the engine. Inaccordance with the present invention it is constructed in such a waythat economical mass production is possible without sacrificingexcellent performance. The compressor diffuser 28 comprises a firstannular element 52 secured to the annular inlet housing l2 through anintegral structural cone 54, as shown in FIG. I. The element 52 has anintegral outer flange 56 having a shoulder 58 which receives the forwardend 60 of housing 32. Housing 32 is secured to flange section 56 by aseries of screws 62. Duct wall 33 is secured to housing 32 so that it isremoved with housing 32.

Referring to FIG. 3, annular element 52 has a smooth aft-facing surface64 defined by an inner diameter D and an outer diameter D The surface 64is defined by straight-lined elements extending radially between theinner and outer diameters. Preferably, the surface 64 lies in a singleplane at right angles to the axis of rotation of the compressor. Asecond annular element 66 abuts the surface 64 and has an integralstructural cone 68 forming a structural component of the engine and anintegral outer flange element 70 with a lip 72 defining an annular flowpath between the housing 32 and the lip for passage of air to chamber 30(see FIG. I). The element 66 has a section corresponding to surface 64which has an inner diameter d, and outer diameter d generallycorresponding to those on surface 64. Inner diameters D and (1 arespaced from the periphery of impeller 22 to form a vanelcss annularinlet 69. This inlet may have an area controlled configuration, asdisclosed in copcnding patent application entitled Compressor DiffuserInlet, Ser. No. 420,203, filed Nov. 29, I973, T. Exley and C. Kuintzleinventors of common assignment with the present application.

As shown particularly in FIG. 2, element 66 has a series of channels 74extending tangentially from the inner diameter d,. These channels 74each have a throat 76 at their inlet end, a first diffusing section 78and a second diffusing section 80. The threat sections 76 are formed bya section of constant channel height and width. The first diffusingsection 78 is formed by a channel having an expanding width and depth.The channel diffusing section 80 is formed by an expanding channel depthand width which are greater than that for the intermediate section 78.As is apparent from FIG. 2, section 80 has a channel width C whichincreases toward the downstream end of the passage. As is apparent fromFIG. 3, the channel depth C,, also increases in the downstreamdirection.

The result of forming channels 74 is a series of wedgelike sections 82in between the channels 74 and having knife edge inlets 84. To permitsecuring of element 66 to element 52 a series of threaded holes 86 areprovided in the wedge-shaped sections 82. These are aligned withsuitable holes in the element 52 to permit the elements to be releasablysecured by bolt assemblies 88. Holes 87, passing through wedges and thecorresponding section of annular housing 52, provide access from oneside of the diffuser to the other. Threaded holes 89 enable additionalbolt assemblies 91 to hold the diffuser section together at that pointand provide means to attach other elements, such as a bleed air conduit.

Element 66 may also be provided with a series of pockets 90 formed inthe downstream section of wedge elements 82 and opening away from thesurface 64, as shown in FIG. 1. These pockets enable the weight of theelement 66 to be substantially reduced without decreasing its strength.

The diffuser 28 is easily manufactured using mass production techniques,Element 66 may be formed from a solid piece of material or cast in roughform. The channels 74 may be formed to very precise tolerances usingstandard milling techniques or electrochemical discharge. Alternatively,the element 66 may be cast from sintered material to produce thefinished dimensions without further machinery, except for the sharpeningof leading edges 84 on the wedges 82.

Once the passages are formed the forwardly facing surfaces of thewedge-shaped elements correspond to the plane of surface 64 and a tightfit is permitted between the two elements. When the diffuser isassembled by securing sections 52 and 66 together it is incorporated aspart of the engine structure. Element 52, in addition to forming oneportion of the diffuser, conveniently forms a portion of the exterior ofthe engine housing. The flange 70 in cooperation with the housing 32conveniently forms a passage for flow of air from the diffuser to theeombustor chamber 30. A diffuser of this type in operation is highlyefficient since the passageway geometry can be controlled to a highdegree of precision. At the same time the diffuser can be made usingstandard mass production techniques, thereby significantly decreasingthe cost of an engine.

It should be noted that the degree of divergence for the above diffuseris significantly greater than that for a prior art channel diffuser. Thereason is that the channels increase both in width and depth while theconventional diffuser channel increases in width only. Thus, a newdimension is available for providing increased divergence.

While a preferred embodiment of the present invention has beendescribed, it should be apparent to those skilled in the art that it maybe practiced in other forms without departing from its spirit and scope.

Having thus described the invention what is claimed as novel and desiredto be secured by letters Patent of the United States is:

l. A compressor diffuser for use with a gas turbine engine having agenerally annular housing comprising: a first annular element having asubstantially smooth face defined by an inner and outer diameter, saidface being defined by straight-lined elements extending radially fromsaid inner to said outer diameter, said first annular element forming aportion of said housing;

a second annular element having an inner and outer diametersubstantially equal to the inner and outer diameter of the face on saidfirst element, said second annular element abutting the face of saidfirst element, said second element having a plurality of tangentiallydirected channels extending from the inner to the outer diameter of saidsecond element to form a series of diffuser passages, said passagescomprising an inlet throat section having a constant height and width, afirst diffusing section having a height and width which expand at afirst rate and a second diffusing section having a height and widthwhich expands at a second faster rate. said widths expanding in thedownstream portion of the channel whereby said diffuser sections providean increasing cross-sectional flow area defined by an increasing channeldepth and increasing channel width and whereby all of the divergence inthe diffuser passageways takes place in said second element.

2. Apparatus as in claim 1 wherein said first annular element is in theform of a flange and said smooth face is in a radial plane.

3. Apparatus as in claim 1 wherein said gas turbine engine comprises aeombustor positioned downstream from said diffuser and an outer housingsurrounding said eombustor, said outer housing being removably securedto the periphery of said first annular element.

4. Apparatus as in claim 3 wherein the first element has a peripheryextending radially outward beyond the periphery of said second annularelemennt, said annular outer housing being attached to the periphery ofsaid first element thereby forming an annular flow path turning airdischarged from said diffuser from a radial to an axial direction.

5. Apparatus as in claim 4 wherein said second element has an aft flangeand a curved lip positioned inward from said annular outer housingthereby defining, in part, said annular flow turning passage.

6. Apparatus as in claim 1 wherein said second annular element is aunitary piece of material having said passages formed in one face as aseries of tangentially directed channels separated by generallywedge-shaped segments forming, in combination with the face on saidfirst element, passages having a generally rectangular cross section.

7. Apparatus as in claim 6 further comprising means for releasablyholding said first and second annular elements against one another.

8. Apparatus as in claim 7 wherein said releasable holding meanscomprises a plurality of bolts extending through one and threaded intothe other of said elements.

9. Apparatus as in claim 6 wherein said second annular element is castand has a plurality of pockets formed in said wedge-shaped portions,said pockets being opened to the face of said second element that isopposite the face in contact with the annular face on said firstelement.

1. A compressor diffuser for use with a gas turbine engine having agenerally annular housing comprising: a first annular element having asubstantially smooth face defined by an inner and outer diameter, saidface being defined by straight-lined elements extending radially fromsaid inner to said outer diameter, said first annular element forming aportion of said housing; a second annular element having an inner andouter diameter substantially equal to the inner and outer diameter ofthe face on said first element, said second annular element abutting theface of said first element, said second element having a plurality oftangentially directed channels extending from the inner to the outerdiameter of said second element to form a series of diffuser passages,said Passages comprising an inlet throat section having a constantheight and width, a first diffusing section having a height and widthwhich expand at a first rate and a second diffusing section having aheight and width which expands at a second faster rate, said widthsexpanding in the downstream portion of the channel whereby said diffusersections provide an increasing cross-sectional flow area defined by anincreasing channel depth and increasing channel width and whereby all ofthe divergence in the diffuser passageways takes place in said secondelement.
 2. Apparatus as in claim 1 wherein said first annular elementis in the form of a flange and said smooth face is in a radial plane. 3.Apparatus as in claim 1 wherein said gas turbine engine comprises acombustor positioned downstream from said diffuser and an outer housingsurrounding said combustor, said outer housing being removably securedto the periphery of said first annular element.
 4. Apparatus as in claim3 wherein the first element has a periphery extending radially outwardbeyond the periphery of said second annular elemennt, said annular outerhousing being attached to the periphery of said first element therebyforming an annular flow path turning air discharged from said diffuserfrom a radial to an axial direction.
 5. Apparatus as in claim 4 whereinsaid second element has an aft flange and a curved lip positioned inwardfrom said annular outer housing thereby defining, in part, said annularflow turning passage.
 6. Apparatus as in claim 1 wherein said secondannular element is a unitary piece of material having said passagesformed in one face as a series of tangentially directed channelsseparated by generally wedge-shaped segments forming, in combinationwith the face on said first element, passages having a generallyrectangular cross section.
 7. Apparatus as in claim 6 further comprisingmeans for releasably holding said first and second annular elementsagainst one another.
 8. Apparatus as in claim 7 wherein said releasableholding means comprises a plurality of bolts extending through one andthreaded into the other of said elements.
 9. Apparatus as in claim 6wherein said second annular element is cast and has a plurality ofpockets formed in said wedge-shaped portions, said pockets being openedto the face of said second element that is opposite the face in contactwith the annular face on said first element.